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Keeping secrets Photons of light beamed between satellites could be the key to future global security, according to scientists at the annual meeting of the American Association for the Advancement of Science being held in Vancouver.

From bank accounts to intellectual property, we all have secrets to hide. Currently information can be encrypted using mathematical terms that are considered very difficult to break with today's computers.

But Professor Raymond Laflamme of the Institute of Quantum Computing (IQC) at the University of Waterloo, Canada, says quantum computers will render today's forms of encryption useless.

"When I think about my credit card, I don't mind what happens in 25 years because it will be obsolete or I will have another one," says Laflamme. "But when I start thinking about my health records going down, I start to get more worried."

"When people have quantum computers, they will be able to come back and decode these messages," he says.

The solution to this is quantum cryptography.

Things act strangely in the quantum world. Quantum entanglement occurs when two particles, such as photons, become linked together and 'dance' in perfect unison even if separated by vast distances; something Einstein referred to as "spooky".

Sharing keys

In quantum encryption two parties named Alice and Bob analyse pairs of entangled photons, which behave the same despite their separation, to create and share a unique key. That key is used to securely encode and decode information. Unlike classical cryptography, the key is truly random and therefore considered unbreakable.

According to Jennewein, each photon can only travel 100 kilometres through an optic fibre before it is absorbed. "That limits applications, particularly in big countries like North America and Australia."

To overcome this hurdle, researchers at IQC have proposed a mission called QEYSSAT, currently under consideration by the Canadian Space Agency.

"We want to build a receiver in space, to send photons from quantum sources on the ground to a satellite," says Jennewein.

Photons sent straight up to a satellite receiver only have to travel through a few kilometres of atmosphere. As the satellite orbits Earth, it makes links with major cities to build a global network.

Waves or particles

One company currently working on quantum encryption is QuintessenceLabs, based at the Australian National University in Canberra. Chief Marketing Officer Chris O'Neil says their approach is slightly different.

"You can treat light like a particle, the single photon approach used in Canada and other parts of the world," he says. "We treat light like a wave, a continuous variable."

"They send and capture a single photon. We send a stream of photons, millions at a time."

Their equipment is cheaper and more readily available than that needed to send and detect single photons. QuintessenceLabs are exhibiting at the RSA cryptography conference in San Francisco next week.